12 . f (x) : 7x 2x2-3 13. f (x ) : 2-tan (x) 2+tan (x) for y = 3x3 2 14. Find 5x2 15. Find if x3y 3 +2x2y =y. 16. Find dx2 J3 = 2x5 17. A balloon rises at the rate of 7 feet per second from a point on the ground 120 feet from an observer. Find the rate of change of the angle of elevation when the balloon is 350 feet above the ground. 18. A machine is rolling a metal cylinder under pressure. The radius of the cylinder is decreasing at a constant rate of 0.07 inches per second and the volume I is 86n cubic inches. At what rate is the length / changing when the radius r is 1.25 inches? [Hint: V= 12/] 19. Use logarithmic differentiation to find dy/dx for y = 12-9 x>3 20. Find the derivative of y = 3e-7/x4*2